The invention relates to an electro-hydrostatic actuator that is ideally suited to control the positioning of a valve or any other similar device.
More specifically, this invention relates to a compact electrically operated linear actuator integrates all controls and components so rapidly and efficiently heat dissipation and cooling to component parts is provided.
Current demands on power generation systems and valve controls require that the actuators be electrically controlled and include fail safe features. In many countries, linear actuator of the type herein disclosed also require certification when employed in an environment where an explosion might take place as for example in controlling valves utilized in gas or oil pipelines or in certain processing plants where volatile chemicals are used in the process. In order to gain certification, many of the actuators are housed in rather bulky complex structures, external power supply and controls that are costly to construct and difficult to service and maintain in the field. Typically, the electronic control of the actuator is designed to be located in separate remote housing having a non-hazardous controlled environment. The cabling between the actuator and the controller can be relatively long which can lead to signal transmission loses and other related difficulties.
The invention presently here provides a solution to electrical control actuation within a compact package designed to meet uniform cooling and protection for use in hazardous environments.
In U.S. Pat. No. 2,631,431 to Gerbe, there is disclosed an electrohydraulic actuator in which an electric motor is located in a tank filled with oil. The motor is equipped with a hollow shaft and the shaft of a pump impeller is slidably contained within the hollow motor shaft. The impeller can turn with the motor shaft while at the same time moving longitudinally along the axis of the motor shaft. The pump impeller is situated inside a hollow piston that is secured to a piston rod. The piston rod extends upwardly and passes out of the tank through the top wall of the tank. In operation, the motor drives the impeller at a speed so as to increase the pressure of the oil on one side of the piston to a level wherein the piston and piston rod are displaced upwardly to reposition any type of device that is secured to the piston rod. A weight or spring is used to return the piston to its home position when the motor is de-energized.
Although the Gerbe device provides for improved motor cooling, the electronic controls for the motor are situated at a location remote from the tank housing and is therefore subject to all the problems associated with transmission lines of any appreciable length. Furthermore, because the electrical unit associated with the actuator must be housed in its own non-hazardous container, the system is costly to maintain.